(a) Field of the Invention
The present invention relates to a swing-arm door, and in particular, to a vertical rotation shaft assembly for a swing-arm type door in which shaft misalignment due to wear is avoided.
(b) Description of the Related Art
Commonly, two types of exit doors for buses are adopted, a swing-arm door and a bi-fold door. The bi-fold door consists of two panels fastened together with a hinge or hinges such that the door is opened by a trailing panel being folded to a leading panel. The swing-arm door consists of a panel suspended by a curved arm attached to a rotating door so as to be opened by operation of a swing arm.
FIG. 1 is a partial cross-sectional view showing a prior art vertical rotational shaft assembly of a swing-arm door.
The vertical shaft assembly is fixedly mounted to a vehicle body, and as shown in FIG. 1, comprises a vertical shaft 1 surrounded by an exterior pipe 3 so as to slide up and down therein. To enhance the movement of the vertical shaft 1, a sliding pipe 4 is interposed between the vertical shaft 1 and the exterior pipe 3, and a coil spring 5 is mounted around a lower portion of the vertical shaft 1.
This vertical shaft assembly, however, has a drawback in that the sliding pipe 4 is worn by frequent friction with the rotational vertical shaft 1 so as to generate a gap between the shaft 1 and the sliding pipe 4 such that the operation of the swing-arm door becomes unstable and the durability of the door is degraded.
The present invention has been made in an effort to solve the above problems of the prior art.
It is an object of the present invention to provide a vertical shaft assembly capable of preventing swing-arm door malfunctions due to wearing of the sliding pipe.
To achieve the above object, the vertical rotation shaft assembly for the swing-arm type door according to a preferred embodiment of the present invention comprises an upper rotational shaft extended from the cylinder as a piston rod and a lower rotational shaft inserted into an edge of the door plane, the lower rotational shaft being coaxially arranged with the upper rotational shaft.